In a wireless communication system to which the present invention can be applied, a femtocell Advanced Base Station (femto ABS) is a small-size version of a macrocell Advanced Base Station (macro ABS) and performs most functions of the macro ABS. The femto ABS may be installed in an area covered by the macro ABS or may be installed in a shadow area that is not covered by the macro ABS.
A wireless communication system including femto ABSs is described below with reference to FIG. 1. FIG. 1 illustrates a configuration of a wireless communication system including femto ABSs. As shown in FIG. 1, the wireless communication system includes femto ABSs 110, a macro ABS 120, a femto network gateway (FNG) 130, an access service network (ASN) 140, and a connectivity service network (CSN) 150. The macro ABS 120 is a general base station of the conventional wireless communication system.
Each femto ABS 110 is a small-size version of the macro ABS 120 and performs most functions of the macro ABS 120. The femto ABS 110 directly connects to a transmission control protocol/Internet protocol (TCP/IP) network and operates independently as the macro ABS 120 does. The coverage of the femto ABS 110 is about 0.1 to 30 m and each femto ABS 110 can accommodate about 10 to 20 mobile stations. The femto ABS 110 may also use the same frequencies as the macro ABS 120 or may use different frequencies from the macro ABS 120.
The femto ABS 110 can cover an indoor or shadow area that is not covered by the macro ABS 120 and can support high data rates. The femto ABS 110 may be installed in an overlay fashion in a macrocell and may also be installed in a non-overlay fashion in an area that is not covered by the macro ABS 120.
The femto ABS 110 is classified into two types. The first type is a closed subscriber group (CSG) femto ABS and the second type is an open subscriber group (OSG) femto ABS. The CSG femto ABS groups mobile stations capable of accessing the CSG femto ABS and assigns a CSG ID to the group of mobile stations and allows only mobile stations assigned the CSG ID to access the CSG femto ABS. The OSG femto ABS is a base station which can be accessed by every mobile station.
As a gateway that controls the femto ABS 110, the FNG 130 is connected to the ASN 140 and the CSN 150 through an Rx interface and an Ry interface. The femto ABS 110 can receive a service from the CSN 150 through the FNG 130 and a mobile station connected to the femto ABS 110 can receive services of functions such as authentication and IP Multimedia Subsystem (IMS) from the FNG 130 or the CSN 150.
The CSN 150 provides the mobile station with connection to an application service such as the Internet or VoIP service. The ASN 140 controls the macro ABS 120 and manages connection between the macro ABS 120 and the CSN 150.